In the manufacture of conventional vertical memory devices, a spacer is generally formed on the sidewall of a contact opening before a conductive stud fills up the opening, so as to enhance the insulation between the conductive stud and the other conductive materials or contacts. However, the spacer is usually formed without a perfect vertical profile, which causes the conductive stud has a larger width on its top portion than on the bottom portion. In other words, due to the imperfect profile of the spacer, the conductive stud generally has an overhang around its top portion. As shown in FIG. 1, a conventional conductive stud 10 with the overhang 14 is formed because of the imperfect profile of the spacer 12. Because of the existence of overhang 14, the space between two wires or contacts will be reduced, and the process widow of manufacturing subsequent interconnections is accordingly decreased, which usually leads to short circuit of devices.
Implementing extra processes, such as etching and deposition, is usually a conventional way to eliminate the overhang. For example, when a conductive stud with an overhang is formed, portions of the spacer and the dielectric layer encircling the conductive stud are etched to expose the overhang. Then, a conductive layer is deposited to cover the overhang and then planarized, so as to remove the overhang. These extra processes complicate the manufacture procedure and increase the cost of production. Therefore, there is a need to provide a method of forming a conductive stud free of overhang at low cost.